On Wed, 26 Sep 2018 at 15:17, Peter Zijlstra <[email protected]> wrote: > > On Wed, Sep 26, 2018 at 12:33:25PM +0200, Vincent Guittot wrote: > > On Wed, 26 Sep 2018 at 11:35, Valentin Schneider > > > > library I use) has some phase where it spawns at lot of tasks at once to > > > do > > > some setup (busybox, shutils, bash...). Some of those tasks are pinned to > > > a > > > particular CPU, and that can lead to failed load_balance() - and to make > > > things > > > worse, there's a lot of idle_balance() in there. > > > > > > Eventually when I start running my actual workload a few ~100ms later, > > > it's > > > impacted by that balance_interval increase. > > > > > > Admittedly that's a specific use-case, but I don't think this quick > > > increase > > > is something that was intended. > > > > Yes, this really sounds like a specific use-case. Unluckily you find a > > way to reach max interval quite easily/every time with your test > > set-up but keep in mind that this can also happen in real system life > > and without using the newly idle path. > > So if it's a problem to have a interval at max value for your unitary > > test, it probably means that it's a problem for the system and the max > > value is too high > > > > Taking advantage of all load_balance event to update the interval > > makes sense to me. It seems that you care about a short and regular > > balance interval more that minimizing overhead of load balancing. > > At the opposite, i'm sure that you don't complain if newly idle load > > balance resets the interval to min value and overwrite what the > > periodic load balance set up previously :-) > > Well, we've excluded newidle balance from updating such stats before. So > in that respect the patch proposed by Valentin isn't weird. > > Consider for example: > > 58b26c4c0257 ("sched: Increment cache_nice_tries only on periodic lb") > > In general I think it makes perfect sense to exclude newidle balance > from such stats; you get much more stable results from the regular > balance.
Ok so in this case we should exclude all update of the interval during newly idle and not only some of them
